Dissociation between deficits in explicit procedures and implicit processes in the visual-spatial and the phonological systems during reading acquisition.

Two clinical studies are reported of children with proficient word-reading skill despite severe performance deficits of explicit visual recognition of the lateral ("mirror image") orientation of letters. In dissociation from their deficit in such an explicit procedure, the children had proficient implicit processing of letters that change identity with lateral reversal, as shown in nonword reading, and in letter-naming accuracy and reaction times relative to a normal comparison sample of children. In one child, another dissociation was also apparent in the phonological system. He had a severe performance deficit in explicit processing of phonemes (phonemic awareness) but was proficient in grapheme-phoneme recoding for reading. The findings indicate that it is possible for both the visual-spatial coding and the phonological systems to function in reading acquisition with impaired performance of explicit procedures in each system while maintaining proficient development of reading skill.